a) Field of the Invention
The present invention relates to a method of measuring a temperature, and more particularly to a method of indirectly measuring a substrate temperature under heat treatment.
b) Description of the Related Art
Various types of heat treatments are carried out during semiconductor manufacture processes. The substrate temperatures at heat treatments affect the performances of final products. Impurity ions doped in semiconductor are activated and diffused depending on the temperatures and time durations of heat treatments carried out after the ion implantation. Wiring layers such as an Al layer deposited on a semiconductor substrate reflow depending on the temperatures and time durations (and types) of heat treatments carried out during or after the wiring layer deposition.
Sputtering is generally used for forming a wiring layer such as an Al layer and an Al alloy layer (alloy of Al and, Si or Si--Cu). For planarization of the surface of a film deposited by sputtering, reflow is often used in which the deposited film is heated to fluidize it. A reflow temperature of Al or Al alloy is usually 400 to 500.degree. C. High temperature sputtering is also used in which not only reflow is carried out after sputtering, deposition and reflow are both carried out during sputtering by heating the substrate.
In the following, a substrate heating process used for forming an Al or Al alloy film will be described by way of example without any limitative sense. For simplicity, Al and Al alloy are collectively called an Al alloy.
Some Al alloy wiring layers may have unsatisfactory surface flatness or low resistance. If the surface flatness is poor, the precision of succeeding photolithography may lower or the step coverage of a film formed thereafter may degrade. If a desired low resistance is not obtained, the circuit performance may degrade or it may cause breakage of a wiring.
In order to avoid such phenomena and maintain good product quality and manufacture yield, it is important to control process parameters. The substrate temperature at heat treatment is one of the important parameters.
FIGS. 5A and 5B illustrate a typical one of conventional methods of measuring a substrate temperature. A semiconductor substrate 51 is placed on a heater 55, and temperatures are measured at representative points on the semiconductor substrate 51 during heat treatment. The tips of thermocouples 52a-52d, 52f (collectively indicated at 52) are fixed to these representative points at which temperatures are measured.
In the example shown in FIGS. 5A and 5B, four thermocouples 52a-52d are fixed to the semiconductor substrate in the radial directions thereof and another thermocouple 52f is fixed at the center thereof. The lead wires of the thermocouples are bundled together and guided to the outside via a feed through 53 to be connected to thermocouple terminals of a pen recorder 57. The pen recorder 57 records the temperatures measured with the thermocouples 52 as a function of time.
This measuring method can measure the temperatures of the substrate at the points where the thermocouple is positioned, in real time during heat treatment. The measured signals (voltage signals) are automatically recorded by the recorder. The pen recorder usually has thermocouple terminals to which the thermocouples are connected, so that it can directly record the measured signals as temperatures.
With this method, it is necessary for temperature measurement to mount thermocouples on a semiconductor substrate. Furthermore, for a process to follow, the thermocouples once mounted are required to be dismounted.
The number of thermocouples to be mounted on a semiconductor substrate to measure the surface temperature is limited inevitably. The limited number of thermocouples means the limited number of temperature measuring points. It is therefore not so easy to measure a fine temperature distribution in the surface of a semiconductor substrate.
If the mount state of a thermocouple is bad, the reliability of measurement results is lost and measurement reproductivity becomes poor.
If a wiring layer is sputtered and heat treatment for a reflow process is consecutively performed, thermocouples cannot be mounted on the semiconductor substrate unless it is moved to the outside after the sputtering process. Although the reflow process is required to be executed consecutively after the sputtering, this reflow process should be interrupted by transferring the substrate to the outside and mounting thermocouples. Therefore, high fidelity reproduction of the processes becomes difficult because of this temperature measurement.